While KEO's employees and exact history are unknown, they were implied to be founded in the 1800s when the British Empire colonized Kyrat. After the country got its independence from The British Empire, presumably after the Second World War due to the amount of weapons styled from that time period, KEO was allowed to stay and soon Kyrat's post-colonial economy flourished as they became dependent on gold mining.
During the 1960's, KEO's mines began to dry up, causing KEO to lose funds. Soon afterwards, the mines were completely exhausted, so KEO went bankrupt and Kyrat's economy spiraled into free fall. This lead to chaos and civil unrest during the 1970's and fueled the Nationalists cause, eventually resulted in First Kyrati Civil War.
The Royal Guard now occupies the mines ever since Kyrat came under Pagan Min regime grip. Amita claims the mines are still exhausted and are stripped bare. KEO assets such as trucks are still being used by Royal Guard to deliver supplies.